How to get the calling method information in Java

I was wondering around in a huge code base trying to figure out whats going on.
I wouldn’t say it was a bad code base, but it was done by a single geeky programmer who never cared about the readability because I guess he never thought anyone else would ever try to read it. Anyway, I could see all these meaningful log messages coming out from it but I didn’t know from where. I think he never heard of log4j or anything like that but luckily he used a class like this:

public class LogHelper{    
   public static void log(String log){

      System.out.println(log);  
   }
}

and used it like this:

public class X  { 
     public void doA() { 
        Logger.log("doing A"); 

        //..         
        //..         
        Logger.log("done doing A");
     }

     public void doB() {
	Logger.log("doing B");
        // 
        //

        Logger.log("done doing B");
     }
}

So he called this static log method from all over the code base to do the logging.
And the log looked like this:

   doing A
   doing B
   done doing B
   done doing A

I desperately wanted to know which class/method/line was calling this method like I am used to in log4j.

Then I thought the calling Thread has this information. The question is how can I get it! After playing a bit with stack information, I came up with this:

public static String getCallingMethodInfo() {  
  StackTraceElement[] stackTrace ;

  try{
      throw new Exception();  
  }
  catch (Exception e) { 
    stackTrace = e.getStackTrace();
  }

  if(stackTrace != null && stackTrace.length >= 2) {

     StackTraceElement s = stackTrace[2];  
  
     if(s != null) {

        return s.getClassName() + ".(" + s.getMethodName() +"):["+ s.getLineNumber() + "] -:";

     } 
  }

  return null;
}

So finally the log method looked like this:

public class LogHelper {  
 public static void log(String log){

      String caller = getCallingMethodInfo();  
      System.out.println(caller + ": " + log);

   }
}

So, finally the logs looked like this:

  X.(doA):[5]-: doing A
  X.(doB):[14]-: doing B
  X.(doA):[9]-: done doing A
  X.(doB):[18]-: done doing B

In jdk 1.5 you can actually get the stack information like this:

Thread.currentThread().getStackTrace()

but unfortunately I was working with a 1.4 codebase. But Throwing an exception and catching it back did the trick 🙂

Having said all that, It will be an insane idea to put this code to production. But can be very helpful when you are trying to understand the code.

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